1. Field of Invention
The present invention relates to a chain guide connecting a cam sprocket and a crank sprocket. More particularly, the present invention relates to a chain guide that reduces friction loss by making the cross-section of a contact portion that contacts the back of a chain in the chain guide a convex curved surface.
2. Description of Related Art
A vehicle engine generally has a combustion chamber that generates power by combusting fuel, and a valve train including an intake/exhaust valve train that controls intake air and exhaust gas disposed at the combustion chamber. The valve train opens/closes the combustion chamber in accordance with a crankshaft.
The crankshaft needs to drive the camshaft so that the valve train can be operated, and the camshaft is connected with the crankshaft via a chain 30. Further, a chain tensioner 45 and a chain guide 40 are applied in case a difference of phase between the camshaft and the crankshaft is changed because the valves cannot be opened/closed according to combustion timing.
In this way, when the chain 30 and the chain tensioner 45 are equipped, the chain 30, as shown in FIG. 1, is wound around a crank sprocket 20 and a cam sprocket 10.
A tensioner arm 41 is disposed at a side of the chain 30 so that the tensioner arm 41 adjusts the tension of the chain 30 by being controlled by the chain tensioner 45, and the chain guide 40 is fixed at the other side of the chain 30.
In a chain driving system that converts a rotation force of the crankshaft 20 generated by combusting fuel into rotation of the camshaft, as shown in FIG. 1, if the engine speed increases, the moment of inertia and the driving torque of a revolving body in an engine increase, and a vertical load in a friction portion increases.
Therefore, frictional resistance between the chain 30 and the tensioner arm 41 and frictional resistance between the chain 30 and the chain guide 40 coincide, leading to deteriorated fuel consumption.
FIG. 2A is a partially cut-away perspective view of a conventional chain guide and FIG. 2B is a cross-sectional view of an “A”-“A” line of FIG. 2, and we can see that a back 35 of the chain 30 contacts the chain guide 40 at a contact surface.
Because energy loss increases as the contact surface increases, a reduction of the operation area of the frictional force is needed in order to reduce the energy loss.
An increase in the thickness of an oil film is also needed because a sufficient thickness of the oil film between the chain 30 and the chain guide 40 makes the frictional coefficient small.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.